Methyl trans-2-methyl-2-pentenoate is an α,β-unsaturated ester. It is formed during the photolysis of pyrazoline. Methyl cis- and trans-2-methyl-2-pentenoate are formed during the pyrolysis of cis- and trans-3,5-dimethyl-3-carbomethoxy-Δ1-pyrazoline.